In order to inject active substances, syringes are used that have a piston-holding cylinder whose front end is provided is with a central or offset tapered mount over which can be slipped the tapered seat of an end fitting of a metallic needle. Such syringes are used in large numbers as so-called single-use syringes that are disposed of after use.
The needle and its end fitting are sealed in a sterile packing and held in a protective cap formed as a quiver-like sleeve having an open end whose internal dimension is such that it can fit tightly over the outer surface of the tapered mount. The doctor and medical staff are thus protected when unpacking the needle and fitting it to the syringe end mount. Once the tapered end fitting is secured to the end mount of the syringe, the protective cap is pulled off so that an injectable substance can be drawn in and then used for a subcutaneous, intravenous, or intramuscular injection or so as to draw body fluids, normally blood, from the patient. In order to prevent needle sticks after use, the cap is fitted back over the front needle end, the end fitting of the needle is pulled off the syringe, and the needle inside the protective cap is thrown out. The protective cap is made of plastic and is formed such that it does not bend even when severely stressed nor can it expose the needle tip. There remains however as a result of the small inside diameter of the protective cap the danger that the sharp needle end misses it to create a substantial danger of injury and a high risk of infection.
Medical personal are normally working very quickly and are occupied with the patient, so that the needle is set aside after use. The used needle is left unprotected on the table and is often tossed as an “open needle” into the trash. When the trash is emptied by the cleaning personnel the needle pokes easily through the plastic garbage bag and can easily injure the personnel dealing with the trash since the needles and syringes are not visible from outside.
In order to prevent this, German 3,904,559 (US equivalents U.S. Pat. Nos. 4,820,277, 4,909,791, and 4,909,972) proposes a protective sleeve for the needle of a syringe that is formed of two pivotal jaws that can be locked to each other so as to enclose the syringe needle in a tube-like space. The jaws are pivoted on the body of the syringe, on a separate adapter, or on the bases of a specially designed syringe needle. The disadvantage of this solution is that it is technically complex and, in particular relative to standard production costs, expensive since the half-shell jaws must be locked together.
It has been proposed for injection needles that the needle be mounted on the piston in its full-forward position so that it can be drawn back into the empty cylinder. A complex coupling is needed that not only increases the cost of the end product but also makes using the needles after use more difficult, requiring at least particular attention and careful handling when fitting the needle end fitting to the piston.
It has further been suggested to provide a longitudinally slidable sleeve on the syringe body that is pulled forward after the syringe is used and closed so that the needle point is covered. The disadvantage of this system is that the diameter of the syringe in increased (by double the wall thickness of the sleeve), the tapered end fitting cannot be mounted at the very end of the syringe body, and it does not rule out the accidental insertion of a finger into the sleeve. Even such an embodiment is not only expensive because of the considerable material used, but in particular because of the closure.